Press for metal stamping



Jan. 8, 1952 A. K. NowAK 2,581,434

PRESS FOR METAL STAMPING Filed Nov. 5, 1947 6 Sheets-Sheet l FLYWHEEL AIR CLUTCH I O OTOR l9 70 67 8 8/ 16 7/ 69 62 PILOT PUMP B 2 r2 a 23 a I B f 65 TANK- 40 T3 runnrx 35 62 VA v: 1 39c 44 $0 t 26 5- i 7 //i4 .r/ -7 Pi? ZFREFILL I 3' SSURE 2 H 8 vaLva 3/ fi v uc H 2 3 J 32 men-um; VALVE CONTROL 0 SELECTOR- men 0!? RUN I26 0 Q CLUTCH INCHINq-UP 0R nowu HYDRAULIC u 0 CYCLE BUTTON l2 0 0 START AND war IDLE POSITION Jan. 8, 1952 A. K. NOWAK 2,581,434

PRESS FOR METAL STAMPING Filed Nov. 5, 1947 6 Sheets-Sheet 2 Al CLUTCH FLYWHEEL MOTOR 2/ .22 o

. 19 69 a] l6 ,8 7 f 62[ DILOT PUMP I B 2 0 5" 5 5 3 27 a7 :3 38 1= g I FE :zc 35 a 'i I f 60 9 28 30 I I 5/ 58 H 422 HOLDING VALVE I PULL BACK VALVE m5:- L Pmsnu. VALVE q I 3 I23 s I a 6 I a I] [I H 2 g I I fi END OF APPROACH STROKE QM W15 Jan. 8, 1952 A. K. NOWAK 2,581,434

PRESS FOR METAL STAMPING Filed Nov 5, 1947 6 Sheets-Sheet 3 9 AIR CLUTCH FLYWHEEL PILOT PUMP HOLDING VALVE PREFILL VALVE POSITION JUST BEFORE END OF DOWN STROKE /w/w W MM/ m Jan. 8, 1952 A. K. NOWAK 2,

PRESS FOR METAL STAMPING Filed Nov. 5, 1947 6 Sheets-Sheet 4 FLYWHEEL A; n? CLUTCH MOTOR PILOT PUMP HOLDING VALVE PULL BACK VA VE PREF'ILL VALVE 6 POSITION JUST BEFORE START F RETURN MOVEMENT OF SLIDE Jan. 8, 1952 A. K. NOWAK 2,581,434

PRESS FOR METAL STAMPING Filed Nov. 5, 1947 6 Sheets-Sheet 5 AIR CLUTCH FLV WHEEL 15" Q MOTOR PILOT VALVE 84 a3 V P LL BACK VALVE PREHLI. VALVE VIIIIIIIIIIA NEARING END OF UPSTROKE Jan. 8, 1952 A. K. NOWAK PRESS FOR METAL STAMPING Filed Nov. 5, 1947 CONTROL ROD- VARIABLE. MAX. STROKE 30" CONTEOL. R21- IO PER "UN- 6 Sheets-Sheet 6 m 6 szconos P CYCLES WITH MAX. SHUT HEIGH "C" CYCLE I0 PER MIN. ow: IN 6 55.

T5 AND MA X. DRAWS.

"N" CYCLE m 4ssc. l5 FER MIN.

20 SROKE ADJ. D

N*C. PRESSES, SAME srRm-s PER MIN. ONE m 6 sec.

CYCLES WITH MIN. SHUT HEIGHT nowrv Ia APPR. ZO'Z-VARIABLE ECCEA IDLE APPROACH PRESSURE RETURN I 2 3 N DRAW TIM! 2.7 se

DRAW TIME Patented Jan. 8, 1952 UNITED STATES PATENT OFFICE PRESS FOR METAL STAMPING Alois Karl Nowak; Evanston, Ill. Application November 5, 1947, Serial No. 784,123 24 Claims. (01. 60-545) This invention relates to power presses and has ifOl' its principal object:

To make a fixed stroke drive such as an eccentric deliver a longer stroke to a tool carrying slide and vary that stroke to suit diiferent die sets;

To increase the number of stroke cycles per minute, and hence the output of the press;

To make it practicable to use an eccentric or the like with a stroke approximately the same as the maximum depth of the draw part while providing the necessary or appropriate daylight; and

To reduce the draw speeds and increase the draw time and make it possible to use common drawing steel sheets while maintaining present production speeds, which now require special steels to prevent rupture.

Further objects and advantages of the invention will appear as the disclosure proceeds and the description is read with the accompanying drawings, in which- Fig. 1 is 'a diagrammatic view of the essential features of the press showing the parts in idle position;

Fig. 2 is a similar view showing the parts in the position they assume at or near the end of the approach stroke;

Fig. 3 is a similar view showing the parts in the position they assume just before the end of the down stroke or draw stroke;

Fig. 4 is a similar view showing the parts in the position they assume just before the start of the return movement of the slide;

Fig. 5 is a similar view showing the parts in the position they assume as the slide approaches the end of the up stroke; and

Figs. 6, 7, and 8 are charts showing the comparative curves of a conventional press and the new press embodying the present invention.

GENERAL DESCRIPTION The press includes a bed l8 adapted to receive a tool II to cooperate with a tool l2 carried by a slide l3 arranged to reciprocate in guides M. A motor l5 drives a countershaft l3 having a flywheel I! and an air clutch I8 and driving a main shaft l9 through gearing 2B. The main shaft is equipped with an eccentric 2I cooperating with an eccentric strap 22 and a rod 23 to drive a ram 24 having a double acting piston 25 in a main or ram cylinder 26 between the stufiing box 21 and'the closed head 28.

" A passage 29 connects the main cylinder below the piston 25 with the upper end of an auxiliary or press cylinder 30 fitted with a double acting piston 3| connected by a rod 32 with the slide and operating between a stufiing box 33 and the piston 3| of the press cylinder.

Associated with the cylinders is a tank 35 for hydraulic liquid, which is connected by a passage 36 with the press cylinder 30 below the piston 3|, and it, in turn, is connected by a passage 31 with the main cylinder 26 above the main piston 25, and that passage is equipped with a spring seated check valve 38. The main cylinder above the piston 25 is also connected with the tank 35 by a passage 39 equipped with a spring seated check valve 40 in a chamber 4| on the side of the main cylinder.

The press cylinder 30 is connected with the tank 35 through a prefill valve casing 42 having a spring seated prefill valve 43, the stem 44 of which is associated with (shown superimposed upon) a piston 45 in a cylinder 46 formed in the upper end of the prefill valve casing 42 and in communication with the main cylinder 26 through a passage 41. The piston 45 has an operating rod 48 passing out through the top of the cylinder 45 to actuate the switch I.

The passage 36 connecting the tank 35 with the press cylinder 30 below the piston 3! has a pullback valve including a casing 50, a valve head 5|, and a stem 52 with a superimposed piston 53 operating in a cylinder 54 formed in the upper end of the casing 50. The piston 53 has an operating rod 55 adapted to actuate a switch B.

The passage 36 also has a holding valve 5'5 in .a casing 58 and normally seated by a spring 59 to prevent flow from the passage 36 through an .auxiliary holding valve passage 60 to the tank 35, or vice versa.

The pull-back valve and the holding valve are controlled by a hydraulicsystem including a pilot pump 62 having an intake pipe 63 leading from the tank 35 and an outlet pipe 64 leading back to the tank 35 but equipped with a pressure limiting valve 65 adapted to maintain a suitable pres- .sure in the control system.

A pipe 66 connected with the outlet 64 of the pilot pump is, in turn, connected by a pipe 5! with the cylinder 68 of a solenoid valve A, and that cylinder is connected with the tank 35 by a pipe 69 and with the cylinder 54 of the pull-back valve by pipe 10. The solenoid valve A has a piston valve H in the cylinder 88 normally biased. by the spring I2 and operated on suitable occasion by a solenoid in a familiar manner.

The pipe 66 connected with the outlet 54 of the pilot pump 65 is also connected with a pipe J it, which, in turn, is connected by a pipe ":4 with a cylinder '35 of solenoid valve H having a pie ton valve it normally biased by a spring ll but operated on occasion by a solenoid in a familiar manner.

The slide I3 is equipped with a cam 80 adapted to operate a limit switch D as the slide approaches the work to initiate the stroke of the mechanical drive.

A control lever ilLpivoted and fulcrumed at 82 on the main shaft I9, is connected by a link 83 and suitable pivots with the ram 24, and is operated in unison with it but with a multiplied movement, depending upon the design. The control lever 8| has a connecting rod 84 through which it operates a control rod 85 having an upper cam 83 adapted to operate a switch E and a lower cam 87 adapted to operate a switch G. The rod moves through suitable guides 88, two of which are equipped with brackets 39 in which is mounted a screw 99 carrying the switches D and E and by which they are adjusted inunison.

OPERATION Idle position '(shown on sheet 1) The flywheel I1 ;is rotating and the air clutch I8 is disengaged. The eccentric 21 with its plunger 2 1 isidle in the-up position. The check valves 38 and 40 at each side of the plunger in the main cylinder 26 are seatedby their springs. The prefill valve .43 on top of press cylinder 33 is held open by its pilot piston under pressure within the main cylinder above the piston communicated to the pilot cylinder 46 through the passage 41. The solenoid A is energized, placing .its piston valve in position where the pilot pressure of the pump 62 is blocked and the pilot cylinder 54 above the pull-back valve is connected with the tank through the discharge pipe 69. The pull-back valve 5| is closed by its spring. The solenoid H is de-energized, thereby placing its piston valve in position where the tank connection is blocked and the pilot pressure is admitted behind the holding valve '57, holding it firmly against its seat. The control link 8| on the eccentric shaft anditscontrolrod are in their up position. The press piston 3| and the slide i3 are in their up position.

Starting the cycle of operation The operator starts the cycle of the press by pushing a cycle button I00, which causes the solenoid A to be de-energized, permitting the piston valve H to shift to its upward position, blocking the tank connection 69 and admitting pilot pressure from the pump 62 into'the pilot cylinder 54 of the pull-back valve. The pull-back valve is opened, thereby connecting the auxiliary cylinder beneath the piston 3! with the tank 35, and gravity forces theslide and the pieton downward, the fluid beneath the piston being discharged into the-tank.

The downward movement of the press piston 3! produces a partial vacuum in the press cylinder 38 above the piston, and atmospheric pressure on the hydraulic fluid in the tank opens the prefill valve #3 against its closing spring, and hydraulic fluid flows from the tank into the press cylinder 38 above the piston, keeping it filled as the piston descends during its approach or .clos- (See Fig. 2.)

The draw or working stroke As the slide descends, the cam strikes the ing stroke.

limit switch D :(Fig. 2), which is so adjusted that a if piston 3i and checking the slide, which latter ends the creation of partial vacuum in the auxil- .iary cylinder above the piston 3|, and the prefill valve is closed automatically by its spring.

The stems or operating rods 48 and 55 of the valves I and B close an electric circuit, which operates the well known solenoid air valve, admitting air into the clutch l8 and causing it to engage, thereby starting the rotation of the eccentric.

Operating the limit switch D has also energized the solenoid H, which relieves the holding valve of the pilot pressureand-permits it tocush ion the drop of the slide and upper die when the pull-back valve closes .(Fig. .3). The spring .59 of the holding valve will, of course, be adjusted according to the weight to be cushioned.

The rotation of the eccentric 2! moves the plunger piston downwardly, and the displacement beneath it is forced through the passage 29 into the press cylinder above the piston 31, forcing the latter and the slide downward against the work. (Fig.3.) During this movement, the displacement in the cylinder 30 beneath the piston 33! forces the hydraulic fluid :through the holding valve into the tank 35.

The displacement in the main cylinder 26 by the downward movement of the main piston 25 produces a partial vacuum above piston .25, which is filled by a fluid under atmospheric pressure from the tank through the check valve 40.

As the ram 24 approaches the down position, the control rod brings the cam 8'! into operating contact with the-switch 'G. :(Fig. '3.) (The ratio between the arms of the lever 81 corresponds to the difference between the effective upper area of the piston 25 and the lower area of the piston 3|, which, for example, may beassumed to be 3:1. This would give the stroke of the control rod three times the length of the stroke of the ram 24. Hence, while the ram and slide make their pressure stroke, the control rod with its cams .86 and 8.1 makes a longer stroke, three times as long.)

At the end of the down stroke, the cam 8.1 cpcrates the limit switch G, which de-energizesithe solenoid H of the holding valve, shifting the piston valve into a position blockin .the exhaust connection and admitting the pilot pressure hehind the holding valve '51. Switch G simultaneously .de-energizes the solenoid A, shifting the piston valve into position, blocking the exhaust connection, and admitting pilot pressure into the pilot cylinder 54 of the pull-back valve 5!, opening that valve. (See Fig. 2.)

Dwell at bottom of stroke (sheet 4) The eccentric 2.1 and the plunger 24 begin their up stroke, releasing the pressure on the fluid in the system, and the pilot pressure of the pump 62 opens the pull-back valve bl. As the piston 25 of the plunger moves upwardly, its displacement in the cylinder 26 above the piston forces liquid through thecheckvalve38 and the passage 31', the cylinder 30, and passage 38 through the pull-back valve into the tank 35.

Hence, the piston 3I and with it the slide and the upper die I2, will remain or dwell in the dowr position on the work.

The displacement in the cylinder 26 below the piston will produce a partial vacuum in the cylinder, which will be filled by atmospheric pressure forcing hydraulic fluid from the tank through the prefill valve.

The up stroke of the plunger 24 produces a corresponding but more rapid up stroke of the control rod 85 and the upper cam 86, and eventually brings that cam into operating contact with the switch E.

Return stroke of the slide (sheet 5) Operating the limit switch E energizes the solenoid A, shifting the piston valve into position, blocking the pilot pressure, and exhausting the pilot cylinder 63 into the tank, and the pull-back valve 5! is closed by its spring, arresting the flow of fluid from the passage 36 into the tank.

The continued upward movement of the piston 25 with the eccentric promptly builds up pressure above the piston 25 in the cylinder 26, which is communicated from the passage 31 to the cylinder beneath the piston 3|, and that piston with the slide and upper die begins the upward movement.

The pressure in the main cylinder 26 above the piston 25 is transmitted through the passage 47 and opens the prefill valve 43, allowing free flow from above the piston 3| into the tank. (See Fig. 5.)

During the remainder of the upward movement of the eccentric, the displacement above the piston 25 passes into the cylinder 30 below the piston 3| and moves that piston with the slide with a speed determined by the ratio between the upper area of the piston 25 and the lower area of the piston 3|, heretofore assumed to be 3:1.

The upward movement continues until the eccentric reaches its top position, when a cam or other familiar device (not shown) operates another limit switch, releasing the air clutch as the parts reach the assumed position shown in Fig. 1.

The closing action of the springs on the prefill and pull-back valves is augmented by the flow of hydraulic fluid, and hence the closing is very quick and positive as distinguished from the slow acting valves of prior presses.

COMPARISON WITH CONVENTIONAL MECHANICAL PRESS (Figs. 6, 7, and 8) In Fig. 6, the symmetrical curve III) indicates the cycle of a conventional press (C) having a 20-inch stroke eccentric with 10 cycles per minute or 1 in 6 seconds.

The unsymmetrical curve III indicates the cycle a press made according to this invention (N) with a 10-inch stroke eccentric, a cycle in 3.2 seconds, or 19 per minute. And the sharp incline H2 indicates the quick approach followed by the maximum draw II3, the dwell H4, and the rapid up stroke I I5. (With this same setting, any less draw can be made, in which case quick approach would remain the same for the setting of the switch D but the remainder of the approach would be governed by the movement of the eccentric.)

This chart (Fig. 6) shows the curves and cycles with the presses set for maximum shut height and maximum draw.

Fig. '7 gives a comparison between the same conventional press and a press made according to this invention with a 10-inch stroke eccentric and set for a minimum shut height. The cycle of the N press is 4 seconds or 15 per minute as against I9 per minute of the conventional press.

Fig. 8 shows a comparison of the two presses having the same number of strokes per minute. The shaded areas I20 and I2I indicate the corlGSpOl'ldll'lg portions of the 10-inch maximum draw stroke and indicate the relatively greater drawing time and slower drawing speed provided by the N press of this invention.

Thus, these charts show how the new press of this invention makes it possible to increase the number of stroke cycles per minute, and hence the output, or to increase the drawing time and reduce the drawing speed with the same number of stroke cycles per minute, or increase the drawing speed some and to a lesser extent the number of stroke cycles per minute.

Alongside the charts in Figs. 6 and 7, the control rod and the adjustable mounting for the limit switches D and E are illustrated, and a comparison between Figs. 6 and 7 indicates how the length of the stroke of the press made according to this invention may be adjusted to suit the varying requirements of the draw and different sets of dies.

SLIDE ADJUSTMENT, UP OR DOWN The adjustment of the slide up or down to vary the height of the opening between the top of the bed and the face of the slidethe shut heightwith this press is accomplished with means similar to that disclosed in my prior application Ser. No. 770,033, filed August 22, 1947.

In the diagram, Fig. 1, a solenoid operated inching valve F, shown at the lower right, is connected to the branch pipe 13 by a pipe I22 and to the connection 36 by a pipe I23, and there is a return pipe I24 to the tank 35 which serves both the inching valve F and the piston valve of the holding valve H. The inching valve is operated by the buttons I26 on the control board I21 (Fig. 1). Pressing one of those buttons will add fluid to the system and lower the slide while pressing the other will reduce the fluid in the system and correspondingly raise the slide.

In a press such as illustrated in the diagrams 1-5 with a 10-inch stroke eccentric, it will be satisfactory to set the limit valve 65 to 500 pounds, and thus maintain in the pilot system supplied by the pump 32 a constant pressure of that amount available by operating the several valves A, H, and F.

PRESSURE RELIEF VALVE In order to limit the maximum pressure and therefore the maximum stress that can be placed upon the press, the system is provided with a pressure relief valve I30 which may be arranged to be operated by a solenoid C controlling communication between the system and the tank 35. For convenience in indicating the pressure during any part of the operation, the system is provided with a pressure gauge I3 I.

I claim:

1. In a press, a slide, a mechanical drive ineluding a reciprocable element to which a varying force is mechanically applied with the stabilizing assistance of a fly wheel and a hydraulic transmission between the slide and the drive including a main cylinder, a ram in the main cylinder, a piston connected with the slide, an auxiliary cylinder for the piston in hydraulic connection with the main cylinder, a tank for hydraulic fluid in communication with both cylinders, valve means for said communication, means to operate said valve means to place said auxiliary cylinder in communication with said tank to lower the slide by gravity and fill the auxiliary cylinder, means actuated by the slide to start the mechanical drive, and means actuated by the mechanical drive for returning the slide to its raised position during the upstroke of the reciprocable element.

2. In a press, a slide, a mechanical drive and a hydraulic transmission between the slide and the drive including a main cylinder, a ram in the main cylinder, a piston connected with the slide, an auxiliary cylinder for the piston in hydraulic connection with the main cylinder, a tank for hydraulic fluid in communication with both cylinders, valve means for said communication, means to operate said valve means to place said auxiliary cylinder in communication with said tank to lower the slide by gravity and fill the auxiliary cylinder, means actuated by the slide to start the mechanical drive, and means actuated by the mechanical drive to operate said valve means on the up stroke.

3. In a press, a slide, a mechanical drive and a hydraulic transmission between the slide and the drive including a main cylinder, a ram in the main cylinder, a piston connected with the slide, an auxiliary cylinder for the piston in hydraulic connection with the main cylinder, a tank for hydraulic fluid in communication with both cylinders, a spring seated pull-back valve and a spring seated prefill' valve for said communication, control means for opening the pull-back valve to initiate the approach stroke of the slide, means actuated by the slide during the approach stroke to eflect the closing of the pull-back valve and start the mechanical drive on its down stroke, and

means actuated by the mechanical drive during its up stroke to open the pull-back valve to initiate the up stroke of the slide.

4. In a press, a slide, a mechanical drive and a hydraulic transmission between the slide and the drive including a main cylinder, a rain in the main cylinder, a piston connected with the slide, an auxiliary cylinder for the piston in hydraulic connection with the main cylinder, a tank for hydraulic fluid in communication with both cylinders, valve means for said communication, means to operate said valve means to place said auxiliary cylinder in communication with said tank to lower the slide by gravity and fill the auxiliary cylinder, and limit means actuated, one by the slide during its approach stroke to initiate the down stroke of the mechanical drive, and one actuated by the mechanical drive during its up stroke to initiate the up stroke of the slide.

5. In a press, a slide, a mechanical drive and a hydraulic transmission between the slide and the drive including a main cylinder, a ram in the main cylinder, a piston connected with the slide, an auxiliary cylinder for the piston in hydraulic connection with the main cylinder, a tank for hydraulic fluid in communication with both cylinders, valve means for said communication, means to operate said valve means to place said auxiliary cylinder in communication with said tank to lower the slide by gravity and fill the auxiliary cylinder, and limit means actuated, one by the slide during its approach stroke to initiate the down stroke of the mechanical drive, and one actuated by the mechanical drive during its up stroke to initiate the up stroke of the slide, said limit means being adjustable simultaneously to vary the shut height of the press.

6. In a press, a slide, a mechanical drive including a reciprocable element to which a varying force is mechanically applied with the stabilizing assistance of a fly wheel and a hydraulic transmission between the slide and the drive including a main cylinder, a ram in the main cylinder, a double acting piston connected with the slide, an auxiliary cylinder for the piston in hydraulic connection with the main cylinder, a tank for hydraulic fluid in communication with both cylinders, valve means for said communication, means to operate said valve means to place both sides of said piston in communication with said tank to lower the slide by gravity and fill the auxiliary cylinder, and a holding valve in the communication between the lower part of the auxiliary cylinder and the tank to cushion the descent of the slide.

7. In a press, a slide, a mechanical drive and a hydraulic transmission between the slide and the drive including a main cylinder, a ram in the main cylinder having a double acting piston, an auxiliary cylinder, a double acting piston in the auxiliary cylinder and connected with the slide, a fluid connection between the main cylinder below the piston and the auxiliary cylinder above the, piston, a tank, for hydraulic liquid, a fluid onnecti n. b twe n the ank and the auxiliary cylinder above the pist n. a pri sea ed prefill valve for the last mentioned connection, a fluid connection between the main cylinder above the piston and the auxiliary cylinder below the piston, a fluid connection between the tank and the auxiliary cylinder below the piston, a spring seated pull-back valve therein, means to open the pull-back valve to initiate the approach stroke of the slide, means actuated by the slide during its approach, stroke to initiate the down stroke of the ram piston, and means actuated by the me,- chanical drive during the up stroke of the ram piston to initiate the up stroke of the slide.

8. In a press, a slide, a mechanical drive and a hydraulic transmission, between the slide and the drive including a, main cylinder, a ram in the main cylinder having a double acting piston, an auxiliary cylinder, a double acting piston in the auxiliary cylinder and connected with the slide, a fluid connection between the main cylinder below the piston and the auxiliary cylinder above they piston, a tank for hydraulic liquid, a fluid connection between the. tank and the auxiliary cylinder above the piston, a spring seated preflll valve for the last mentioned connection, a fluid connection between the main cylinder above the piston and the auxiliary cylinder below the piston, a fluid connection between the tank and the auxiliary cylinder below the piston, a spring n seated pull-back valve therein, means to open the pull-back valve to initiate the approach stroke of the slide, means actuated by the slide during its approach stroke to initiate the down stroke of the ram piston, and means actuated by the mechanical drive during the up stroke of the ram piston to initiate the up stroke of the slide, said last two means including limit devices adjustable simultaneously.

9. In a press, a slide, a mechanical drive including a reciprocable element to which a varying force is mechanically applied with the stabilizing assistance of a fly wheel and a hydraulic transmission between the slide and the drive including a main cylinder, 2. ram in the main cylinder, a piston connected with the slide, an auxiliary cylinder for the piston in hydraulic connection with the main cylinder, a tank for hydraulic fluid in communication with both cylinders, means between the tank and the auxiliary cylinder to permit the slide to descend independently of the ram and to automatically fill the auxiliary cylinder as the slide descends, and means actuated by the mechanical drive for returning the slide to its raised position during the upstroke of the reciprocable element.

10. In a press, a slide, a mechanical drive and a hydraulic transmission between the slide and the drive including a main cylinder, a ram in the main cylinder, a piston connected with the slide, an auxiliary cylinder for the piston in hydraulic connection with the main cylinder, a tank for hydraulic fluid in communication with both cylinders, means including a spring seated pull-back valve to permit the slide to make an approach stroke independent of the ram, means including a prefill valve to fill th auxiliary cylinder from the tank as the slide so moves, means actuated by the slide during its approach stroke to initiate the draw stroke of the ram, and means actuated by the mechanical drive during the up stroke of the ram to close the pull-back valve.

11. In a press, a slide, a mechanical drive and,

a hydraulic transmission between the slide and the drive including a main cylinder, a ram in the main cylinder, a piston connected with the slide, an auxiliary cylinder for the piston in hydraulic connection with the main cylinder, a tank for hydraulic fluid in communication with both cylinders, means including a spring seated pull-back valve to permit the slide to make an approach stroke independent of the ram, means including a prefill valve to fill the auxiliary cylinder from the tank as the slide so moves, means actuated by the slide during its approach stroke to effect the closing of said valves to initiate the draw stroke of the ram, and means actuated by the mechanical drive during the up stroke of the ram to open the pull-back valve.

12. In a press, a slide, a mechanical drive and a hydraulic transmission between the slide and the drive including a main cylinder, a ram in the main cylinder, a piston connected with the slide, an auxiliary cylinder for the piston in hydraulic connection with the main cylinder, a hydraulic tank in communication with the auxiliary cylinder, valve means for said communication, means to operate said valve means to place said auxiliary cylinder in communication with said tank to lower the slide by gravity and fill the auxiliary cylinder, means actuated by the slide to effect closing of said valve means and start the mechanical drive, and a holding valve associated with said connection to balance the slide.

13. In a press, a slide, a mechanical drive and a hydraulic transmission between the slide and the drive including a main cylinder, a ram in the main cylinder having a double acting piston, an auxiliary cylinder, a double acting piston in the auxiliary cylinder and connected with the slide, a fluid connection between the main cylinder below the piston and the auxiliary cylinder above the piston, a tank for hydraulic liquid, a fluid connection between the tank and the auxiliary cylinder above the piston, a spring seated prefill valve for the last mentioned connection, a fluid connection between the main cylinder above the piston and the auxiliary cylinder below the piston, a fluid connection between the tank and the auxiliary cylinder below the piston, a spring seated pull-back valve therein, means to open the pull-back valve'to initiate the approach stroke 01' the slide, means actuated by the slide during its approach stroke to initiate the down stroke of the ram piston, and a holding valve to relieve the pressure below the piston in the auxiliary cylinder.

14. In a draw press, the combination of a slide, an intermittently operated mechanical drive for the slide including a device for applying variable pressure during the draw stroke, an extensible connection between the drive and the slide, means independent of said drive for extending said connection to move the slide from full open position through a substantial part of its approach stroke, means responsive to a predetermined extension of said connection for starting the mechanical drive, and means for returning the slide to said full open position.

15. In a draw press, the combination of a slide, an intermittently operated mechanical drive for the slide including a device for applying variable pressure during the draw stroke, an extensible connection between the drive and the slide, means independent of said drive for extending said connection to move the slide from full open position through a substantial part of its approach stroke, means for locking the connection in said extended position, means for applying the mechanical drive to the slide through said locked extended connection, and means for retracting the connection and returning the slide to full open position.

16. In a draw press, the combination of a slide, a mechanical drive for the slide including a device for applying variable pressure during the draw stroke, an extensible connection between the drive and the slide, means independent of said drive for extending said connection to move the slide from full open position through a substantial part of its approach stroke, means for locking the connection in said extended position, means for applying the mechanical drive to the slide through said locked extended connection, and means for retracting the connection and returning the slide to full open position, said last named means including a speed multiplication device.

17. In a draw press, the combination of a slide, a mechanical drive for the slide including a device for applying varying pressure during the draw stroke, an extensible connection between the drive and the slide including a fluid column, means for varying the amount of fluid in said column to thereby change the effective length of said extensible connection, valve means adapted to seal egress of fluid from said column to form thereby a solid fluid column connection between said drive and said slide, means for opening said valve means at the start of the press cycle to permit the slide to fall by gravity through a substantial part of its approach stroke, and means for closing said valve mean and substantially simultaneously starting the mechanical drive in response to movement of the slide to the limit of its approach stroke.

18. In a draw press, the combination of a slide. a mechanical drive for the slide including a flywheel-stabilized device, an extensible connection between the drive and the slide including a fluid transmission device having a first set of piston and cylinder elements operatively connected to the drive and a second set of piston and cylinder elements operatively connected to the slide, a pair of fluid conduits connecting the hydraulic spaces above and below the piston of one of said s ts with. th hydrauli spaces belowand abov re pec i ly, he p o of said c nd. e the ef" f ti p s n rea exp s o one o sai hrdr-aulic spaces associated with said first set oi piston and cylinder elements being different than the piston area exposed to the communicating hydraulic space n the second se of p st n a ylinder ele nts, whereby.- the strokes oi sai wo se s of pis on and cylinder elemen s are unequal in at. least one direction of movement.

19. The combination as set i th in. claim 1. in which a fluid reservoir is in communication through separate passageways with both of said conduits, and valve means in. said passageway-s tor varying the amount of fluid in said conduits and hydraulic spaces for extending and re ractin said extensible connection.

20. In a press, a slide, a mechanical drive for the slide having harmonic motion, a hydraulic transmission between the slide and the drive in.- cluding a ram, a hydraulic pull-hack for the slide, a tank for hydraulic fluid in communication with the transmission and the pull-hack, valve. means for said communication, control means to operate the valve means to vent the pull-back to the tank to lower the slide by gravity and, to open the connection between the tankand the hydraulic transmission, and means responsive to, a predetermined downward movement. of the slide to start the mechanical drive.

21. In a press, a slide, a mechanical drive .for the slide having harmonic motion, a hydraulic transmission between the slide and the drive in cluding a ram, a hydraulic pull-back for the silde, a tank for hydraulic fluid in communication with the transmission and the pull-back, a pull-back valve for the communication between the hydraulic pull-back and the tank, and a prefill valve for the communication, between the tank and the hydraulic transmission.

22. In a press, a slide, a mechanical drive for the slide havingharmonic motion, a hydraulic transmission between the slide and the drive including a ram, a hydraulic pullsback for the slide, a tank for hydraulic fluid in communieation with the transmission and the pulleliack, valve means for said communication, and control means constructed and arranged to open communication between the tank and b th h pull-back and the hydraulic transmission iorthe approach stroke, to close communication be,- tween the tank and the transmission during the drawing stroke, and to open communication he-e tween the tank and transmission and close the communication between the tank and the pullback for the return stroke.

In a p s. a sli e, a reciprocat n driv t r he s ide ha in her-ic ni moti r a y raul transmission t ee the. drive d th slide d e a i de a d. a pi W n said. c lnd l', a hydraulic pull-back associated with the transmission, a hydraulic tank in communication wit e t ansm ssi n and t e p -bac an valve means constructed and arranged for intermittently opening and closing said communication to vent the pull-hack to the tank for an approach stroke of said slide and simultaneously vent the transmission to the tank to charge the transmission for a subsequent draw stroke, and thereafter to close communication between the pull-back and the tank and vent the transmission for a return stroke.

24. In a draw press, the combination of a slide, an intermittently operated mechanical drive for the slide including a device for applying variable pressure during the draw stroke, an exteneible connection between the drive and the slide, means independent of said drive for extending said connection to move the slide from full open position through a substantial part of its approae; stroke, means responsive to a predetermined extension of said connection for starting the mechanical drive, a hydraulic. transmission between the slide and the drive and including a cylinder and a piston therein, valve means to supply fluid to the transmission during the approach stroke, and force actuated valve means to vent; said transmission during the return of said sli e to said full open position.

ALOIS KARL- NOWAK.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 631,789 Greenwood Aug. 29, 1899 1,774,245 Strout Aug. 26, 1930 1,930,155, Wiedmann Oct. 10, 1933 2,227,279 Smith Dec. 31, 1940 2,299,686 Ernst Oct. 20, 1942 2,392,6e4 Camerota Jan. 8, 1946 2,403,912 Doll July 16, 1946 2,405,537 Werner et al. Aug. 6, 1946 2,409,254 Conzelman Oct. 15, 1946 2,448,327 Rode Aug. 31, 1948 FOREIGN PATENTS Number Country Date- 60,958 Germany Feb. 13-, 1892 100,646 Germany Jan. 5, 1,899 

